At a time of manufacturing a semiconductor wafer (hereinafter, referred to as wafer) or a time of manufacturing a device using the wafer, an end part (edge part) of the wafer may be damaged or chipped by being contacted with another component or a wafer holding member in some cases. Furthermore, the wafer may also be cracked because of the scratch or chip. Probability of this scratch or chip in the end part of the wafer is considered to have a relation with a shape of an end surface of the wafer (so-called edge profile part). For this reason, it is important to correctly measure an edge profile of a disk-shaped measurement target represented by the wafer. It should be noted that the shape of the end surface herein is a profile in a thickness direction (one-dimensional direction) of the wafer, that is, a cross-sectional shape in the thickness direction, which is hereinafter referred to as edge profile.
A representative example of a measurement method for the edge profile is a nondestructive inspection method (SEMI-MF-928-0305 Specification Method B) regulated by Semi Standard which is a standard specification established by an industry organization related to semiconductor manufacturing apparatuses/materials (Semiconductor Equipment and Materials International: hereinafter, referred to as SEMI). This nondestructive inspection method is a method including transmitting light to the chamfer processed end part of the disk-shaped wafer in a direction substantially parallel to the respective front and rear surfaces of the wafer (first direction), picking up a projection image of the wafer by a camera from a direction opposite to the light transmitting direction, and measuring the shape of the end surface of the wafer on the basis of the projection image (hereinafter, referred to as light projection measurement method). A contour of a projection image obtained through this light projection measurement method represents a cross-sectional shape of the end surface of the wafer (a cross-sectional shape cut in the thickness direction).
The light projection measurement method is, for example, illustrated as a shape detection method based on a shape detector for detecting the cross-sectional shape of the wafer in Patent Document 1. Also, in Patent Document 2, in the light projection measurement method, an optical system for preventing generation of contour blurriness or diffraction stripes in a projection image is proposed.
FIG. 3(a) shows an example of the projection image (black shadow part) obtained by picking up an image of an end surface of a wafer 1 through the light projection measurement method.
Also, a main objective of the measurement of the edge profile is to evaluate whether or not the end surface shape falls into an allowable range with respect to a previously set design shape (suitability). For this reason, in the measurement of the edge profile, normally, with respect to the projection image of the wafer end surface, a previously set image processing is executed to calculate index values of the end surface shape and the suitability is determined depending on whether or not the calculated index values fall into allowable ranges. The index values include, for example, a chamfer width k of the end surface of the wafer, a chamfer angle θ, a chamfer radius rm (also referred to as edge R, etc.) and the like.
FIG. 4 is an explanatory diagram for describing an example of the index values of the edge profile of the wafer. As shown in FIG. 4, the chamfer width k is a width from a border position Q1 (or Q2) of the front or rear surface (mutually substantially parallel surfaces) of the wafer and a chamfered part E (end surface) of the end part to a tip of the chamfered part (end surface) (a length in the direction parallel to the front or rear surface (radius direction of the wafer 1)) in the projection image. Also, the chamfer angle θ is an angle defined by an extended line of the front and rear surfaces of the wafer 1 and a tangent line with respect to the surface of the chamfered part E (end surface) in the vicinity of the border position Q1 (or Q2) in the projection image. Also, when the chamfered part E (end surface) is approximated by a circular arc, the chamfer radius rm is a radius of the circular arc.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 7-218228
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-145487